Study On Design And Preparation Of Transition Metal Oxides And Their Composites For Lithium Storage

With the growth of science and technology,and the reduction of traditional fossil energy reserves,new renewable energy emerged as the times require,the development of energy storage equipment is particularly important as almost new energy sources generate intermittent electric energy.Since the birth of lithium-ion batteries?LIBs?,they have attracted much attention because of the excellent energy storage and conversion performance.In the process of the development of LIBs,graphite is still widely used as the anode,whose theoretical capacity is only 372 mAh g^-1,which severely limits the application of LIBs.Transition metal oxides?TMOs?are considered to be one of the most promising anodes,especially for cobalt and manganese oxides.MnCo₂O₄ is a bimetallic oxide containing both cobalt and manganese elements,whose theoretical capacity is 908 mAh g^-1,which possess the advantages of cobalt and manganese oxides,thus show the better electrochemical lithium storage performance.However,the problem of low conductivity and volume expansion during electrode reaction are the two main problems for TMOs anodes.In this paper,the MnCo₂O₄ with special structure was designed and prepared,which was modified to improve its lithium storage property.The ingredient and structure of the composite were characterized,the electrochemical lithium storage properties of the anodes were tested and studied.The research results are as follows:?1?The flower-like MnCo₂O₄ was prepared and MnCo₂O₄@PANI was prepared by in-situ polymerization,after introduce of conductive medium rGO,ternary MnCo₂O₄@PANI-rGO composite was prepared.The lithium storage performance was improved after being modified.On the one hand,the overall electric conductivity of the anode was improved,on the other hand,the buffer area can also be provided for the volume change in the electrode reaction process and the formation of the electrode surface SEI film is suppressed.The results show that the discharge capacity of MnCo₂O₄@PANI-rGO composite is kept at 695 mAh g^-1 after 80 cycles at 500 mA g^-1,and that remains at 745 mAh g^-1 after 1050 cycles.At 1000 mA g^-1,the discharge capacity remains at 448 mAh g^-1 after 1050 cycles,which was higher than that of pure phase MnCo₂O₄ anode.?2?The octahedral MnCo₂O₄ was prepared and the MnCo₂O₄@NC structure was formed by carbonizing the coated PANI,then the MnO₂ lamellar structure was grown on the surface,then the three-layer core-shell structure of MnCo₂O₄@NC@MnO₂ was prepared.This unique structure effectively strengthens the structural stability and the coating of NC greatly improves the electric conductivity,meanwhile,the high capacity manganese dioxide provides more reversible capacity.The results show that the MnCo₂O₄@NC@MnO₂ anode possesses a high discharge capacity of 894 mAh g^-1 after120 cycles at 500 mA g^-1.Even at 1000 mA g^-1,the discharge capacity remains at 839mAh g^-1 after 600 cycles.In addition,this anode possesses excellent rate performance.